Ultrafast vibrational dynamics of small organic molecules in solution

In this paper we present a time-resolved study of the vibrational relaxation after excitation of the asymmetric CH2 stretch vibration of dibromomethane and diiodomethane and the C–H stretch vibration of 1,1,2,2-tetrabromoethane. The experiments were performed in a polar and a nonpolar solvent in order to study the influence of the polarity of the solvent on the relaxation. We observe that in both types of solvent the vibrational energy transfer is successively intra- and intermolecular and that the intramolecular relaxation leads to a shift of the transition frequency of the excited molecular vibration. We discuss the experimentally determined time constants of the relaxation in terms of the energy differences between the molecular vibrations and the interactions with the solvent.